Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity.
LEDs are built on a substrate and are doped with impurities to create a p-n junction. A current flows from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Electrons and holes flow into the p-n junction from electrodes with different voltages. If an electron meets a hole, it falls into a lower energy level and releases energy in the form of a photon. The wavelength of the light emitted by the LED and the color of the light may depend on the band gap energy of the materials forming the multiple quantum well (MQW).
Array LEDs are gaining more attention due to the system level cost advantage of AC array LEDs for general lighting applications. For example, the use of a plurality of LEDS arranged in a series configuration may allow higher voltages, and even AC voltage (i.e. 120V). However, isolating the individual LEDs in the array may be difficult and existing manufacturing techniques may cause leakage currents in the LEDs. These leakage currents may be the result of damage caused by etching during formation of an LED mesa. Reactive ion etching (RIE) may be used to create these mesas and etch the interleaving regions between the mesas or LEDs. These LED mesas are defined to isolate individual LEDs or physically separate the LEDs.
Isolating the various LEDs in an array may separate these LEDs electrically, which allows the individual LEDs to be connected in series. FIG. 1 is a cross-sectional view of a lateral AC LED array in series configuration. The LED array 100 has a buffer layer 102 disposed on a substrate 101. In some embodiments, this buffer layer is made using GaN. An n-type layer 103 is disposed on this buffer layer 102. A multiple quantum well (MQW) 104 and p-type layer 105 are disposed on the n-type layer 103. The p-type layer 105 and n-type layer 103 may be, for example, GaN or AlGaInP. The MQW 104 may be GaInN or AlGaInP. A transparent conductive layer (TCL), such as ITO (indium tin oxide) 106, and a p-contact 107 are disposed on the p-type layer 105. An n-contact 108 is disposed on the n-type layer 103.
Inductively coupled plasma (ICP) etching is usually used to create etched region 109 which separates first LED 111 and second LED 112. This etch region typically removes the p-type layer 105, the MQW 104, the n-type layer 103, and the buffer layer 102, so as to create electrical separation between the adjacent LEDs 111,112. The TCL 106, the p-type 105 and the MQW 104 are also formed at a width less than that of the n-type layer 103, so as to allow attachment of an n-contact 108 on the n-type layer 103.
A connection 110, which may be a metal or conductor, connects the first LED 111 to the second LED 112 and bridges the etched region 109. Each of the first LED 111 and second LED 112 may be located within or on a mesa. The etched region 109 may define the air bridge where the connection 110 connects the n-type layer 103 of the first LED 111 to the p-type layer 105 of the second LED 112.
The connection 110 is conductive and therefore must be isolated from the tiered layers of the LEDs 111, 112. For example, if the connection 110 contacts the n-type layer 103 of the second LED 112, as well as the p-contact 107, the second LED 112 will be short-circuited. To minimize this, the etched region 109 may be hollow or filled with air or a polymer. The entire LED array 100 may be encapsulated in a dielectric layer in one particular embodiment.
In addition, the use of ICP has multiple drawbacks. First, ICP uses complicated etch chemistries, which may be expensive. Second, the ICP leaves damage that may increase leakage currents. Third, ICP potentially limits device density due to the anisotropic etch. Fourth, post-ICP treatments may be required to treat any damage from the ICP, which increases the number of manufacturing steps and lowers throughput. Fifth, the LED mesas may vary in dimension or have different cross-sectional areas due to etching, which affects LED performance.
Accordingly, there is a need in the art for an improved LED structure and methods of LED ion implantation that is cost effective, provides a yield improvement, and improves reliability of LED arrays.